soc: qcom: pdr: Fix the potential deadlock

commit 2eeb03ad9f42dfece63051be2400af487ddb96d2 upstream.

When some client process A call pdr_add_lookup() to add the look up for
the service and does schedule locator work, later a process B got a new
server packet indicating locator is up and call pdr_locator_new_server()
which eventually sets pdr->locator_init_complete to true which process A
sees and takes list lock and queries domain list but it will timeout due
to deadlock as the response will queued to the same qmi->wq and it is
ordered workqueue and process B is not able to complete new server
request work due to deadlock on list lock.

Fix it by removing the unnecessary list iteration as the list iteration
is already being done inside locator work, so avoid it here and just
call schedule_work() here.

       Process A                        Process B

                                     process_scheduled_works()
pdr_add_lookup()                      qmi_data_ready_work()
 process_scheduled_works()             pdr_locator_new_server()
                                         pdr->locator_init_complete=true;
   pdr_locator_work()
    mutex_lock(&pdr->list_lock);

     pdr_locate_service()                  mutex_lock(&pdr->list_lock);

      pdr_get_domain_list()
       pr_err("PDR: %s get domain list
               txn wait failed: %d\n",
               req->service_name,
               ret);

Timeout error log due to deadlock:

"
 PDR: tms/servreg get domain list txn wait failed: -110
 PDR: service lookup for msm/adsp/sensor_pd:tms/servreg failed: -110
"

Thanks to Bjorn and Johan for letting me know that this commit also fixes
an audio regression when using the in-kernel pd-mapper as that makes it
easier to hit this race. [1]

Link: https://lore.kernel.org/lkml/[email protected]/ # [1]
Fixes: fbe639b ("soc: qcom: Introduce Protection Domain Restart helpers")
CC: [email protected]
Reviewed-by: Bjorn Andersson <[email protected]>
Tested-by: Bjorn Andersson <[email protected]>
Tested-by: Johan Hovold <[email protected]>
Signed-off-by: Saranya R <[email protected]>
Co-developed-by: Mukesh Ojha <[email protected]>
Signed-off-by: Mukesh Ojha <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Bjorn Andersson <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>

Author: Saranya R

drivers/soc/qcom/pdr_interface.c

@@ -74,7 +74,6 @@ static int pdr_locator_new_server(struct qmi_handle *qmi,
 {
 	struct pdr_handle *pdr = container_of(qmi, struct pdr_handle,
 					      locator_hdl);
-	struct pdr_service *pds;
 
 	mutex_lock(&pdr->lock);
 	/* Create a local client port for QMI communication */
@@ -86,12 +85,7 @@ static int pdr_locator_new_server(struct qmi_handle *qmi,
 	mutex_unlock(&pdr->lock);
 
 	/* Service pending lookup requests */
-	mutex_lock(&pdr->list_lock);
-	list_for_each_entry(pds, &pdr->lookups, node) {
-		if (pds->need_locator_lookup)
-			schedule_work(&pdr->locator_work);
-	}
-	mutex_unlock(&pdr->list_lock);
+	schedule_work(&pdr->locator_work);
 
 	return 0;
 }